It is known that polyacetylenes are polymers showing the repeating unit CH.dbd.CH.sub.n.
There are already different types of polyacetylenes which differ by their molecular weight and the configuration of the conjugated double bond chains in space (G. Natta, G. Mazzanti and P. Corradini, C.R. Acad. Lincei 25, 3, (1958))--(L. B. Luttinger, Chem. Ind. London 1135 (1960))--(M. Hatano, J. Chem. Soc. Japan, Ind. Chem. Sert., 65, 723 (1962)).
These polyacetylenes are compounds that are insoluble in polar solvents, in particular, water and tetrahydrofuran. Up to now, they have been synthesized by polymerization of acetylene H--C.tbd.C--H on a Ziegler-Natta catalyst (H. Shirakawa and S. Ikeda, Polym. J., 2, 231 (1971))--(H. Shirakawa, Japanese patent No. 73, 32581).
Attempts have been further made to carry out the partial chemical dehydrochlorination of polyvinyl chloride; the methods suggested up to now have generally used, as a reactant, alcoholic potassium hydroxide. The percentage dehydrochlorination of the operation barely exceeds 1 to 5%; it is as high as 16% in only one case described by Wirsen and Flodin (J. Appl. Polym. Sc. 22, 3039 (1979)).
Japanese patent application No. 10 590/65 describes a process for obtaining crystalline polyacetylene by copolymerization of vinyl chloride and acetylene in an inert solvent such as acetone in the presence of a catalyst (azodiisobutyronitrile) followed by a dehydrochlorination under highly vigorous conditions using an inorganic base such as sodium hydroxide. The product obtained shows an infrared spectrum with a characteristic band at approximately 1000 cm.sup.-1.
The inventors have already studied the possibilities of using potassium tertiary butoxide (tBuOK) as a dehydrochlorination reagent for PVC (C.R. Acad. Sci. Paris, 281, 991 (1975) and 290, 65 (1980), for the purpose of studying the distribution of molecular weights by gel permeation chromatography and the distribution of polyene sequences of the dehydrochlorinated products by ultraviolet spectroscopy.
tBuOK, which has a high solubility in tetrahydrofuran (THF) (25 g per 100 g) seemed, indeed, to be a very good dehydrochlorinating agent due to its high basicity and the large size of the tBuO.sup.- anion which minimizes chances of substitution.
This work, however, has not led to the complete dehydrochlorination of PVC; it turns out, indeed (C.R. Acad. Sci. Paris, 281, 991 (1975)), that the UV spectrum of the dehydrochlorination product shows, both through its fine structure and UV absorption maximum (385 nm), the particular characteristics of an incomplete dehydrochlorination of PVC.